The present invention concerns a method to control the feed of the metal charge, in particular scrap or the like, for electric arc furnaces.
More particularly, the invention concerns a method to control the times of feed of the metal charge into an electric arc furnace, which allows reduction of disturbances and perturbations, mainly of the electric type, while at the same time maximizing the charge speed and hence the overall productivity of the furnace.
The invention is applied particularly, but not exclusively, for systems to feed scrap with a continuous charge, although its use is not excluded for systems of intermittent feed, for example of the type with baskets.
In an electric arc furnace for melting metal, the scrap can be fed either intermittently, for example with baskets that load rhythmically with a pre-determined timing, correlated to the duration of the melting cycle, or continuously, normally by a conveyor belt having its outlet end connected with the inside of the furnace.
It is known that, in order to increase the productivity of the furnace, one aims to have a loading speed of the scrap that is as high as possible, in order to obtain the maximum quantity of molten metal in the shortest time possible.
It is also known that every loading of the scrap inside the furnace determines a negative effect on the extent to which the electric arc is covered by the foamy slag, which covers the bath of liquid metal.
In other words, the scrap loaded has a disruptive effect on the level of cover that the slag exerts on the electric arc. This means that, in the case of only a partial cover of the arc, or even no cover at all, a smaller or larger part of the energy irradiated by the arc is dispersed toward the walls and the roof of the furnace, which causes a loss of energy efficiency of the furnace.
In these cases, when a reduction is noticed in the degree of cover of the electric arc, the introduction of the scrap is interrupted, or at least slowed down, in order to allow restoration of a state of quiet inside the furnace, which allows a return to an acceptable level of cover of the electric arc.
However, at present the verification of the state of cover of the electric arc is entrusted to empirical or simply visual techniques, which are not reliable, and which to a large extent depend on the experience and skill of the operators.
All of this can cause, on the one hand, unnecessary reductions in the speed of feed, if it is desired to guarantee that a high energy efficiency is maintained; and, on the other hand, reductions in energy efficiency, if it is desired in any case to maintain a high speed of loading the scrap into the furnace.